Self-powered neutron detectors are known, examples being Treinen et al. U.S. Pat. No. 3,390,270, dated June 25, 1968, Anderson U.S. Pat. No. 3,400,289, dated Sept. 3, 1968 and Shields U.S. Pat. No. 3,787,697, dated Jan. 22, 1974.
In all of the prior art detectors, the emitter has been in the form of a rod or wire having a length substantially greater than its cross sectional area, whether or not the emitter has been made of solid material or in powder form enclosed in an insulating tube. These prior art detectors have been designed to operate in the core of a nuclear reactor, inside of the reactor vessel, such as within the core of a pressurized-water reactor, with the core and the detector on the inside of the vessel.
On the outside of the vessel, as in the case of external instrumentation, the prior art detectors are not sensitive enough to permit their practical use. If their sensitivity is increased by the use of unconventionally used materials, their operating life is shortened to an impractical degree by the burn-up of such materials.
Therefore, for the external instrumentation, using detectors outside of the pressure vessel of a pressurized-water reactor, it has been necessary to obtain neutron flux measurements by the use of ionization chambers requiring a supply by a high-voltage electric current. This is not only objectionable, but, in addition, the use of such an expedient has been troubled by the fact that the ionization chambers are undesirably temperature-sensitive.